Direct access storage devices (DASD) have become part of every day life, and as such, expectations and demands continually increase for greater speed for manipulating data and for holding larger amounts of data. To meet these demands for increased performance, the mechanical assembly in a DASD device, specifically the Hard Disk Drive (HDD) has undergone many changes.
In operation, the hard disk is rotated at a set speed via a spindle motor assembly having a central drive hub. Additionally, there are tracks spaced at known intervals across the disk. When a request for a read of a specific portion or track is received, the hard disk aligns the head, via the arm, over the specific track location and the head reads the information from the disk. In the same manner, when a request for a write of a specific portion or track is received, the hard disk aligns the head, via the arm, over the specific track location and the head writes the information to the disk.
The HDD is very sensitive to shock and vibrations, which cause errors to occur. For example, when a notebook computer is moved, the HDD existing within the notebook computer experiences a shock and/or vibration. In an effort to minimize the shock and vibrations which HDDs experience, manufacturers place shock material around the HDD. This shock material is called soft mounting.
However, the soft mounting does not protect the HDD from vibrations occurring during internal operations. When the HDD does some type of operation, the whole disk drive vibrates. For example, when the head moves in one direction during a seek operation, the whole disk drive reacts and moves in the other direction. This reactionary force causes the disk drive to vibrate, degrading the performance of the tracking accuracy. In order to reduce and/or eliminate errors, it is necessary to keep the head maintained on the same track at all times. However, if there are motions in the disk drive, such as vibrations, then the head can not accurately follow on the same track.
One way to compensate for the vibrating disk drive is to increase the performance of the servo and the actuator by increasing the servo's bandwidth. Servo bandwidth determines the hard disk's capability to reject a disturbance, such as the vibration of the disk drive itself. In order to increase the servo bandwidth, the performance of the actuator must be increased, which means increasing the resonance frequency. However, in order to increase the resonant frequency, it is necessary to make an actuator either rigid, heavy, of a very expensive material, or to control the manufacturing tolerances. In many cases, these options are not available or are too expensive.
Additional, there is a limitation on how much servo bandwidth may be increased. Currently, as track pitches become increasingly smaller, more servo bandwidth will be needed. In the near future, a technology to solve this problem which does not include increasing the servo band width is needed.